The present invention relates to a photothermographic material, more precisely, a photothermographic material that shows little residual color in the absence of substantial decoloration and provides an image of high definition.
Photothermographic materials have been proposed since old days and described in, for example, U.S. Pat. Nos. 3,152,904, 3,457,075, and B. Shely, xe2x80x9cThermally Processed Silver Systemsxe2x80x9d in Imaging Processes and Materials, Neblette, 8th Ed., Ed. by Sturge, V. Walworth and A. Shepp, page 2, 1969. Photothermographic materials generally have a photosensitive layer containing a catalytic amount of photocatalyst (e.g., silver halide), a reducing agent, a reducible silver salt (e.g., silver salt of an organic acid) and a toning agent for controlling silver color tone, which are typically dispersed in a binder matrix. After being exposed imagewise, photothermographic materials are heated at an elevated temperature (e.g., 80xc2x0 C. or higher) and thereby an oxidation/reduction reaction is caused between the silver halide or the reducible silver salt (functioning as an oxidizing agent) and the reducing agent to form a black silver image. The oxidation/reduction reaction is promoted by the catalytic action of a latent image of silver halide produced by the exposure. Therefore, the black silver image is formed in the exposed area.
Heat development has an advantage of easy and quick processing because it does not require processing solutions as used in the wet development processing. In recent years, simple and quick development processing is desired in the field of photographic techniques, in particular, photography for medical and printing use. Since wet development processing has substantially reached the limit of improvements, image formation methods based on the heat development are noted in the technical fields of, in particular, photography for medical use and printing use.
However, the heat development suffers from various problems that never occur with the wet development.
One of the problems is the problem concerning decoloration of dye. A dye is often added to photographic light-sensitive materials as a filter or for anti-halation or anti-irradiation purpose. A dye is usually added to a non-photosensitive layer and exerts its function upon imagewise exposing. If the dye remains in the photographic light-sensitive material thereafter, the formed image may be colored with the dye. Therefore, the dye is preferably removed from the photographic light-sensitive material during development after the exposure. In the wet development process, the dye can be readily removed from the photographic light-sensitive material with processing solutions. By contrast, it is very difficult (or substantially impossible) to remove the dye in heat development. For light-sensitive materials exposed with near infrared, infrared or red laser rays, in particular, it is necessary to sufficiently prevent irradiation and halation during exposure in order to obtain an image of high definition, and therefore a dye is usually contained in light-sensitive materials to prevent such a phenomenon. However, because it is difficult to remove a dye in heat development, the coloration of image due to the remaining dye particularly causes a problem.
As one class of methods for solving such a problem, there have been proposed methods of decoloring a dye by heating during heat development. For example, U.S. Pat. No. 5,135,842 discloses a method of decoloring a polymethine dye having a particular structure by heating. U.S. Pat. Nos. 5,314,795, 5,324,627 and 5,384,237 disclose methods of decoloring polymethine dyes by using carbanion generators. As another class of methods, Japanese Patent Laid-open Publication (Kokai, henceforth referred to as JP-A) No. 9-146220, JP-A-11-223898 and so forth propose methods of solving the problem by using an invisible dye that has an absorption peak having a narrow half band width in the near infrared region and shows little absorption in the visible region, substantially without providing a decoloration mechanism.
However, there is no effective means for preventing residual color due to a dye with respect to light-sensitive materials exposed with a red laser ray except for use of a complicated decoloration mechanism, and no effective solution has been proposed yet. Therefore, use of the images must be limited, for example, the images are not used as images for appreciation as visible images as described in JP-A-13294, or the images must be changed to those that can be used as images for appreciation as visible images by delaminating the antihalation layer after exposure (even with increase of waste materials). When the coloration with a dye is prevented by utilizing a decoloration mechanism in a light-sensitive material exposed with a red laser ray, mentioned as problems are insufficient decoloration of the dye, decoloration of the dye during storage of photothermographic materials due to insufficient stability of the dye and so forth. For example, when a polymethine dye is used for the purpose of prevention of irradiation etc., the polymethine dye decomposes during heat development after light exposure and decolored to some extent. However, since the decomposition products of the polymethine dye have light-absorbing property to a certain extent, the docoloration becomes insufficient and thus residual color of images (especially in highlight portions) poses a problem. Furthermore, there is also a problem that a dye once decolored may recolor due to contact with an acid or the like. When decoloration of dye is attained by using a complicated reaction mechanism, there is also caused a problem that there should be various by-products in the light-sensitive material due to the complicated reaction mechanism and they degrade handling property of the light-sensitive material after the heat development.
The present invention was accomplished in view of the aforementioned various problems, and its object is to provide a photothermographic material suitable for light exposure with a red laser ray that can provide an image having sufficient definition without residual color after development and superior handling property.
The inventors of the present invention assiduously studied about dyes and as a result, they obtained a finding that irradiation upon exposure with a red laser ray could be sufficiently prevented by using a dye in an aggregated state showing sharp absorption (having a narrow half band width), and such a dye showed markedly little absorption for lights within the visible region and thus causes no practical problem of remaining color tint. They accomplished the present invention based on this finding.
That is, in order to achieve the aforementioned object, the present invention provides a photothermographic material having a support, at least one photosensitive layer containing a silver halide and a reducing agent and a non-photosensitive layer containing aggregates of a dye, wherein a transmission absorption spectrum of the aggregates has a maximum absorption wavelength within the range of 600-750 nm. The photothermographic material of the present invention preferably further contains a non-photosensitive silver source (more preferably, silver salt of an organic acid). Further, the photothermographic material of the present invention preferably contains the aggregates of a dye in the form of aqueous microparticles containing hydrophilic colloid in the non-photosensitive layer.
As preferred embodiments of the present invention, there are provided the aforementioned photothermographic material, wherein the maximum absorbance peak in the transmission absorption spectrum of the aggregates has a half band width of 100 nm or less; the aforementioned photothermographic material, wherein the aggregates show a maximum absorbance of 0.15 or less for a light having a wavelength of 400-600 nm before and after heat treatment; and the aforementioned photothermographic material, wherein the aggregates show an absorbance of 0.2 or more for a light of a wavelength for light exposure.
As a preferred embodiment of the present invention, there is provided the aforementioned photothermographic material, wherein the photosensitive layer is disposed on a laminate of the non-photosensitive layer and the support, and as a more preferred embodiment of the present invention, there is provided the aforementioned photothermographic material, wherein the photosensitive layer is disposed on the support side of the laminate.
The dye is preferably a polymethine dye (more preferably a cyanine dye or an oxonol dye). The dye is especially preferably a cyanine dye represented by the following formula (I) or an oxonol dye represented by the following formula (II). 
In the formula (I), Z1 and Z2 each independently represent a nonmetallic atom group required to complete a 5- or 6-membered nitrogen-containing heterocyclic ring, R1 and R2 each independently represent an alkyl group, an alkenyl group, an aralkyl group or an aryl group, L1 represents a methine chain consisting of an odd number of methines, and X represents an anion. a, b and c each independently represent 0 or 1. 
In the formula (II), Y1 and Y2 each independently represent a nonmetallic atom group required to complete an aliphatic ring or a heterocyclic ring, L3 represents a methine chain consisting of an odd number of methines, and Xa represents a proton or a cation.
As preferred embodiments of the present invention, there are provided the aforementioned photothermographic material, which is exposed by using a red laser, and the aforementioned photothermographic material, which is used for forming an image for medical use.
According to the present invention, there can be obtained a photothermographic material that can provide sufficient definition and shows no residual color and superior handling property after development as a photothermographic material for light exposure with a red laser.
The photothermographic material of the present invention will be explained in detail hereafter. In the following description, ranges indicated with xe2x80x9c-xe2x80x9d mean ranges including the numerical values before and after xe2x80x9c-xe2x80x9d as the minimum and maximum values.
The photothermographic material of the present invention has at least one photosensitive layer and at least one non-photosensitive layer, and contains aggregates of a dye in at least one non-photosensitive layer. The aggregates have a maximum absorption wavelength in the range of 600-750 nm, preferably 600-720 nm, more preferably 620-700 nm. Therefore, the maximum absorption wavelength in the transmission absorption spectrum of the photothermographic material of the present invention is preferably in the range of 600-750 nm, more preferably 600-720 nm, further preferably 620-700 nm.
The aggregates show an absorption width at xc2xd of the maximum absorbance peak (i.e., half band width) of preferably 100 nm or less, more preferably 80 nm or less, further preferably 40 nm or less, particularly preferably 25 nm or less, in the transmission absorption spectrum. It is preferred that the half band width of the photothermographic material of the present invention should also be in a similar range.
The aggregates preferably show a maximum absorbance for a light having a wavelength of 400-600 nm of 0.15 or less, more preferably 0.13 or less, further preferably 0.10 or less, before and after heat treatment. It is preferred that the photothermographic material of the present invention in an unexposed state should show a maximum absorbance for the aforementioned wavelength range in a similar range.
The aggregates preferably show absorbance of 0.2 or more for a light of a wavelength for light exposure. The term xe2x80x9clight of a wavelength for light exposurexe2x80x9d used herein means a light of a wavelength at which the photothermographic material is exposed, and it means a light of a wavelength in the range of 600-750 nm, preferably 620-700 nm, for the photothermographic material of the present invention. It is preferred that the photothermographic material of the present invention should also show absorbance for a light of a wavelength for light exposure in the aforementioned range.
In the photothermographic material of the present invention, the photosensitive layer is preferably disposed on a laminate of the non-photosensitive layer and the support, and the photosensitive layer is preferably disposed on the support side of the laminate. That is, a structure in which the non-photosensitive layer containing the aggregates, the support and the photosensitive layer are laminated in this order is more preferred.
The dye used for the present invention exists in the state of aggregates in the photothermographic material.
A dye existing as aggregates forms the so-called J-band and shows a sharp absorption spectrum peak. Aggregation and J-band of dyes are described in various references (e.g., Photographic Science and Engineering, Vol. 18, No. 323-335 (1974)). The absorption maximum of a dye in the J-aggregated state shift to the longer wavelength side compared with the dye as a solution (monomer state). Therefore, it can easily determine whether a dye contained in a layer is in the aggregated state or non-aggregated state by measuring the absorption maximum. As for the dye in the aggregated state, the shift of the absorption maximum from that obtained in the monomer state is preferably 30 nm or more, further preferably 40 nm or more, most preferably 45 nm or more.
Among dyes, there are also compounds that form aggregates only by dissolving or dispersing them in water. Therefore, a non-photosensitive layer containing aggregates of a dye may be formed by only applying an aqueous coating solution or dispersion containing the dye on a support. However, dyes generally do not form aggregates in an aqueous solution, but forms aggregates when gelatin or a salt (e.g., potassium chloride, sodium chloride, barium chloride, calcium chloride, ammonium chloride) is added to an aqueous solution of the dyes. Therefore, a non-photosensitive layer containing aggregates of a dye can be formed by applying, on a support, a coating solution or dispersion formed by adding gelatin to an aqueous solution of a dye or adding a dye to an aqueous solution of gelatin. In such an embodiment, the aggregates of a dye are contained in a non-photosensitive layer as aqueous microparticle dispersion containing hydrophilic colloid.
Further, aggregates of a dye can also be formed as a solid microparticle dispersion of the dye. In order to obtain a solid microparticle dispersion state, a known dispersing machine can be used. Examples of such a dispersing machine include ball mill, vibration mill, planetary ball mill, sand mill, colloid mill, jet mill and roller mill. Medium dispersing machines of vertical type or horizontal type (described in JP-A-52-92716 and International Patent Publication WO88/074794) are preferred. Dispersion operation may be performed in the presence of a suitable medium (e.g., water, alcohol). It is preferable to use a surfactant for dispersion. Anionic surfactants (described in JP-A-52-92716 and WO88/074794) are preferably used. If necessary, anionic polymers, nonionic surfactants or cationic surfactants may be used. After dissolving a dye in a suitable solvent, a poor solvent may be added to obtain microparticulate powder. The aforementioned surfactants can also be used in this case. Further, microcrystals of a dye may be deposited by regulating pH of a solution. Such microcrystals are also aggregates of a dye.
In the present invention, two or more kinds of dyes in the aggregated state may be used. In such a case, one kind of aggregated state may be formed with two or more kinds of dyes, or dyes in two or more kinds of aggregated states may be used together.
Although the dye that can form aggregates, which is used for the present invention, is not particularly limited, polymethine dyes are preferred. Polymethine dyes can be classified into cyanine dyes, melocyanine dyes, arylidene dyes, stilyl dyes and oxonol dyes. These polymethine dyes are defined by the following formulas.
Cyanine dye: Bs=Lo-Bo
Melocyanine dye: Bs=Le=Ak
Arylidene dye: Ak=Lo-A
Stilyl dye: Bo-Le-Ar
Oxonol dye: Ak=Lo-Ae
In the formulas, Bs represents a basic nucleus, Bo represents an onium of basic nucleus, Ak represents a keto type acidic nucleus, Ae represents an enol type acidic nucleus, Ar represents an aromatic nucleus, Lo represents a methine chain consisting of an odd number of methines, and Le represents a methine chain consisting of an even number of methines.
In the present invention, it is preferable to use a cyanine dye or an oxonol dye among the polymethine dyes, and it is still preferable to use a cyanine dye. As the cyanine dye, compounds represented by the formula (I) above are preferred.
In the formula (I), Z1 and Z2 each independently represent a nonmetallic atom group required to complete a 5- or 6-membered nitrogen-containing heterocyclic ring. Another heterocyclic ring, aromatic ring or aliphatic ring may condense to the nitrogen-containing heterocyclic ring. Examples of the nitrogen-containing heterocyclic ring and condensed ring thereof include oxazole ring, oxazoline ring, isoxazole ring, benzoxazole ring, naphthoxazole ring, thiazole ring, thiazoline ring, benzothiazole ring, naphthothiazole ring, selenazole ring, selenazoline ring, benzoselenazole ring, indolenine ring, benzoindolenine ring, imidazole ring, imidazoline ring, benzimidazole ring, naphthoimidazole ring, quinoline ring, pyridine ring, pyrrolopyridine ring, furopyrrole ring, indolidine ring, imidazoquinoxaline ring, quinoxaline ring, oxadiazole ring, thiadiazole ring, tetrazole ring and pyrimidine ring. The nitrogen-containing heterocyclic ring is preferably a 5-membered ring, and more preferably, a benzene ring or naphthalene ring is condensed to the 5-membered nitrogen-containing heterocyclic ring. The nitrogen-containing heterocyclic ring is more preferably a benzimidazole ring, naphthoimidazole ring, benzoxazole ring, naphthoxazole ring, benzothiazole ring or naphthothiazole ring, particularly preferably a benzothiazole ring or naphthothiazole ring.
The nitrogen-containing heterocyclic ring and the ring condensed thereto may have a substituent. Examples of the substituent include an alkyl group, a cycloalkyl group, an aralkyl group, an alkoxy group, an aryl group, an aryloxy group, a halogen atom (Cl, Br, F), an alkoxycarbonyl group, an alkylthio group, an arylthio group, an acyl group, an acyloxy group, an amino group, a substituted amino group, an amido group, a sulfonamido group, a ureido group, a substituted ureido group, a carbamoyl group, a substituted carbamoyl group, a sulfamoyl group, a substituted sulfamoyl group, an alkylsulfonyl group, an arylsulfonyl group, a hydroxyl group, a cyano group, a nitro group, a sulfo group, a carboxyl group and a heterocyclic group. The sulfo group and carboxyl group may be in the form of a salt.
The alkyl group may be linear or branched. The alkyl group preferably has 1-20 carbon atoms. The alkyl group may further have a substituent, and examples of the substituent include a halogen atom (Cl, Br, F), an alkoxy group (e.g., methoxy group, ethoxy group), a hydroxyl group and a cyano group. Examples of the alkyl group (including a substituted alkyl group) include methyl group, ethyl group, propyl group, t-butyl group, hydroxyethyl group, methoxyethyl group, cyanoethyl group and trifluoromethyl group. Examples of the cycloalkyl group include cyclopentyl group and cyclohexyl group. The aralkyl group preferably has 7-20 carbon atoms. Examples of the aralkyl group include benzyl group and 2-phenethyl group. The alkoxy group may be branched or linear, and preferably has 1-12 carbon atoms. The alkoxy group may further have a substituent, and examples of the substituent include an alkoxy group and a hydroxyl group. Examples of the alkoxy group (including a substituted alkoxy group) include methoxy group, ethoxy group, methoxyethoxy group and hydroxyethoxy group.
The aryl group is preferably a phenyl group. The aryl group may further have a substituent, and examples of the substituent include an alkyl group, an alkoxy group, a halogen atom and a nitro group. Examples of the substituted aryl group include p-tolyl group, p-methoxyphenyl group, o-chlorophenyl group and m-nitrophenyl group. The aryloxy group is preferably phenoxy group. The aryloxy group may have a substituent, and examples of the substituent include an alkyl group, an alkoxy group and a halogen atom. Examples of the substituted aryloxy group include p-chlorophenoxy group, p-methylphenoxy group and o-methoxyphenyl group. The alkoxycarbonyl group preferably has 2-20 carbon atoms. Examples of the alkoxycarbonyl group include methoxycarbonyl group and ethoxycarbonyl group.
The alkylthio group preferably has 1-12 carbon atoms. Examples of the alkylthio group include methylthio group, ethylthio group and butylthio group. The arylthio group is preferably phenylthio group. The arylthio group may further have a substituent, and examples of the substituent include an alkyl group, an alkoxy group and a carboxyl group. Examples of the substituted arylthio group include p-methylphenylthio group, p-methoxyphenylthio group and o-carboxyphenylthio group. The acyl group preferably has 2-20 carbon atoms. Examples of the acyl group include acetyl group and butyroyl group. The acyloxy group preferably has 2-20 carbon atoms. Examples of the acyloxy group include acetoxy group and butyryloxy group. The substituted amino group preferably has 1-20carbon atoms. Examples of the substituted amino group include methylamino group, anilino group, and triazinylamino group. The amido group preferably has 2-20 carbon atoms. Examples of the amido group include acetamido group, propionamido group and isobutanamido group. The sulfonamido group preferably has 1-20 carbon atoms. Examples of the sulfonamido group include methanesulfonamido group and benzenesulfonamido group.
The substituted ureido group preferably has 2-20 carbon atoms. Examples of the substituted ureido group include 3-methylureido group and 3,3-dimethylureido group. The substituted carbamoyl group preferably has 2-20 carbon atoms. Examples of the substituted carbamoyl group include methylcarbamoyl group and dimethylcarbamoyl group. The substituted sulfamoyl group preferably has 1-20 carbon atoms. Examples of the substituted sulfamoyl group include dimethylsulfamoyl group and diethylsulfamoyl group. The alkylsulfonyl group preferably has 1-20 carbon atoms. Examples of the alkylsulfonyl group include methanesulfonyl group. The arylsulfonyl group is preferably benzenesulfonyl group. Examples of the heterocyclic group include pyridyl group and thienyl group.
In the aforementioned formula (I), R1 and R2 each independently represent an alkyl group, an alkenyl group, an aralkyl group or an aryl group. Especially, an alkyl group is preferred. The alkyl group may be linear or branched. The alkyl group preferably has 1-20 carbon atoms. The alkyl group may have a substituent, and examples of the substituent include a halogen atom (Cl, Br, F), an alkoxycarbonyl group (e.g., methoxycarbonyl group, ethoxycarbonyl group), a hydroxyl group, a sulfo group and a carboxyl group. The sulfo group and carboxyl group may be in the form of a salt. The alkenyl group may be linear or branched. The alkenyl group preferably has 2-10 carbon atoms. Examples of the alkenyl group include 2-pentenyl group, vinyl group, allyl group, 2-butenyl group and 1-propenyl group. The alkenyl group may have a substituent, and examples of the substituent are similar to the examples of the substituent of the aforementioned alkyl group.
The aralkyl group preferably has 7-12 carbon atoms. Examples of the aralkyl group include benzyl group and phenethyl group. The aralkyl group may have a substituent, and examples of the substituent include an alkyl group (e.g., methyl group, ethyl group, propyl group), an alkoxy group (e.g., methoxy group, ethoxy group), an aryloxy group (e.g., phenoxy group, p-chlorophenoxy group), a halogen atom (Cl, Br, F), an alkoxycarbonyl group (e.g., ethoxycarbonyl group), a halocarbon group (e.g., trifluoromethyl group), an alkylthio group (e.g., methylthio group, ethylthio group, butylthio group), an arylthio group (e.g., phenylthio group, o-carboxylphenylthio group), a cyano group, a nitro group, an amino group, an alkylamino group (e.g., methylamino group, ethylamino group), an amido group (e.g., acetamido group, propionamido group), an acyloxy group (e.g., acetoxy group, butyryloxy group), a hydroxyl group, a sulfo group and a carboxyl group. The sulfo group and carboxyl group may be in the form of a salt. Examples of the aryl group include phenyl group and naphthyl group. The aryl group may have a substituent, and examples of the substituent are similar to the examples of the substituent of the aforementioned aralkyl group.
In the aforementioned formula (I), L1 represents a methine chain consisting of an odd number of methines. The number of methines is preferably 1, 3, 5 or 7, more preferably 3 or 5, particularly preferably 3. The methine chain represented by L1 may have a substituent. The methine having a substituent is preferably the methine at the center (meso position) of the methine chain. Examples of the substituent include an alkyl group, an alkoxy group, an aryloxy group, a halogen atom, an alkoxycarbonyl group, a halocarbon group, an alkylthio group, an arylthio group, a cyano group, a nitro group, an amino group, an alkylamino group, an amido group, an acyloxy group, a hydroxyl group, a sulfo group and a carboxyl group. Two of substituents may bond to form a 5-membered or 6-membered ring.
In the aforementioned formula (I), X represents an anion. Examples of the anion include a halide ion (Clxe2x88x92, Brxe2x88x92, Ixe2x88x92), p-toluenesulfonate ion, ethylsulfate ion, PF6xe2x88x92, BF4xe2x88x92 and ClO4xe2x88x92. In the aforementioned formula (I), a, b and c each independently represent 0 or 1. a and b preferably represent 0. When the cyanine dye has an anionic substituent such as a sulfo group or a carboxyl group and forms an intramolecular salt, c is 0.
As the oxonol dye, compounds represented by the formula (II) above are preferred.
In the aforementioned formula (II), Y1 and Y2 each independently represent a nonmetallic atom group required to complete an aliphatic ring or a heterocyclic ring. The ring completed with Y1 or Y2 is preferably a heterocyclic ring. Examples of the aliphatic ring include indanedione ring. Example of the heterocyclic ring include 5-pyrazolone ring, oxazolone ring, barbituric acid ring, pyridone ring, rhodanine ring, pyrazolidinedione ring and pyrazolopyridone ring. The aliphatic ring and heterocyclic ring may have a substituent, and examples of the substituent are similar to the examples of the substituent of the nitrogen-containing heterocyclic ring completed with Z1 or Z2 in the aforementioned formula (I).
In the aforementioned formula (II), L3 represents a methine chain consisting of an odd number of methines. The number of methines is preferably 3, 5 or 7, more preferably 3 or 5, particularly preferably 3. The methine chain may have a substituent. The methine having a substituent is preferably the methine at the center (meso position) of the methine chain. Examples of the substituent are similar to the examples of the substituent of L1 in the aforementioned formula (I). Two of substituents may bond to form a 5- or 6-membered ring. However, the methine chain is preferably unsubstituted.
In the aforementioned formula (II), Xa represents a proton or a cation. When Xa is a proton, an oxygen atom adjacent to the proton forms a hydroxyl group. Examples of the cation include an alkali metal ion (e.g., sodium ion, potassium ion), ammonium ion, triethylammonium ion, tributylammonium ion, pyridinium ion, tetrabutyl ammonium ion and onium ion.
Specific examples of the polymethine dyes preferably used are shown below. However, the dye used for the present invention is not limited to the following specific examples. In the following specific examples, Ph represents a phenyl group. 
The polymethine dyes can be synthesized by referring to the descriptions of F. M. Harmer, xe2x80x9cHeterocyclic Compounds Cyanine Dyes and Related Compoundsxe2x80x9d, John Wiley and Sons, New York, London, 1964 and JP-A-6-313039.
The photothermographic material of the present invention has a photosensitive layer and a non-photosensitive layer. The aforementioned dye should be contained in at least one non-photosensitive layer. As a preferred embodiment of the present invention, there can be mentioned the photothermographic material in which the non-photosensitive layer containing the dye functions as a filter layer or an antihalation layer. Depending on the position of the non-photosensitive layer, it is classified into (1) an overcoat layer provided on a photosensitive layer (the opposite side of the support), (2) an intermediate layer provided between two or more of photosensitive layers, (3) an undercoat layer provided between a photosensitive layer and a support; and (4) a back layer provided on a side opposite to the photosensitive layer. A filter layer is provided in the photosensitive material as the layer of (1) or (2). An antihalation layer is provided in the photothermographic material as the layer of (3) or (4). In the photothermographic material according to a more preferred embodiment of the present invention, the non-photosensitive layer containing the dye is an antihalation layer, i.e., the non-photosensitive layer is disposed as the layer of (3) or (4), and in the photothermographic material according to a further preferred embodiment, the non-photosensitive layer is disposed as the layer of (4).
As a method for adding the dye to a non-photosensitive layer, a method may be employed which comprises a step of adding a solution, emulsion, solid or microparticle dispersion of the dye, or the dye impregnated in a polymer to a coating solution for the non-photosensitive layer. The dye may also be added to the non-photosensitive layer by using a polymer mordant. These addition methods are the same as those generally employed for the addition of dyes to ordinary photothermographic materials. Polymer latex used for preparation of the dye impregnated in a polymer are described in U.S. Pat. No. 4,199,363, German Patent Laid-open Nos. 25,141,274, 2,541,230, EP-A-029104 and Japanese Patent Publication (Kokoku, hereinafter referred to as JP-B) No. 53-41091. An emulsification method by adding a dye to a solution in which a polymer is dissolved is described in International Patent Publication WO88/00723. Content of the dye in the non-photosensitive layer may be determined depending on the intended use. Generally, it is used in such an amount that optical density (absorbance) should exceed 0.1 when it is measured at the wavelength to be used. The optical density is preferably 0.2-2. The amount of the dye used for obtaining such an optical density is generally about 0.001-1 g/m2.
The photothermographic material will be further explained hereafter.
For the photothermographic material of the present invention, a non-photosensitive silver source can be used. Although any silver source can be used so long as it is non-photosensitive and can supply silver (ion), a silver salt of an organic acid is preferably used. The silver salt of an organic acid is a silver salt relatively stable against light, but forms a silver image when it is heated at 80xc2x0 C. or higher in the presence of an exposed photocatalyst (e.g., a latent image of photosensitive silver halide) and a reducing agent. The silver salt of an organic acid may be any organic substance containing a source of reducible silver ions. Such non-photosensitive silver salts of an organic acid are disclosed in JP-A-10-62899, paragraphs 0048 to 0049, EP0803763A1, page 18, line 24 to page 19, line 37, EP0962812A1, JP-A-11-349591, JP-A-2000-7683, JP-A-2000-72711 and so forth. Silver salts of an organic acid, in particular, silver salts of a long chained aliphatic carboxylic acid having 10-30, preferably 15-28 carbon atoms, are preferred. Preferred examples of the silver salt of an aliphatic carboxylic acid include silver behenate, silver arachidinate, silver stearate, silver oleate, silver laurate, silver caproate, silver myristate, silver palmitate, mixtures thereof and so forth. In the present invention, there is preferably used silver salt of an organic acid having a silver behenate content of 50 mole % or more, more preferably silver salt of an organic acid having a silver behenate content of 80 mole % or more, further preferably silver salt of an organic acid having a silver behenate content of 90 mole % or more, among the aforementioned silver salts of an organic acid. Further, the non-photosensitive silver source may be contained in either a photosensitive layer or a non-photosensitive layer. When Tg of binder together contained in a layer containing the silver source is 40xc2x0 C. or higher, the silver behenate content is preferably 55-85 mole %.
The shape of the silver salt of an organic acid that can be used for the present invention is not particularly limited, and acicular grains, rod-like grains, tabular grains and scaly grains can be mentioned. However, scaly silver salt of an organic acid is preferred for the present invention. Grains of irregular shape such as short acicular grains, rectangular parallelepiped grains, cubic grains or potato-like grains having a ratio of long axis and short axis of 5 or less are also preferably used. These grains of silver salt of an organic acid have a characteristic that they show less fog during heat development compared with long acicular grains having a ratio of long axis and short axis of more than 5. The scaly silver salt of an organic acid is described in detail in JP-A-11-349325. As for the scaly silver salt of an organic acid, if the shape of the organic acid silver salt grain is approximated a rectangular parallelepiped and the sides of the rectangular parallelepiped are defined as a, b and c from the shortest, a can be regarded as a thickness of a tabular grain having a plane having sides of b and c as a main plane. The average of a is preferably 0.01-0.23 xcexcm, more preferably 0.1-0.20 xcexcm. The average of c/b is preferably 1-6, more preferably 1.05-4, even more preferably 1.1-3, particularly preferably 1.1-2.
The grain size distribution of the aliphatic acid silver salt is preferably monodispersed. The term xe2x80x9cmonodispersedxe2x80x9d as used herein means that the percentage of the value obtained by dividing the standard deviation of the length of the short axis or long axis by the length of the short axis or long axis, respectively, is preferably 100% or less, more preferably 80% or less, further preferably 50% or less. The shape of the aliphatic acid silver salt can be determined from a transmission electron microscope image of aliphatic acid silver salt dispersion. Another method for determining the monodispesibility is a method involving obtaining the standard deviation of a volume weight average diameter of the aliphatic acid silver salt. The percentage (coefficient of variation) of the value obtained by dividing the standard deviation by the volume weight average diameter is preferably 100% or less, more preferably 80% or less, further preferably 50% or less. As a measurement method, for example, the grain size (volume weight average diameter) can be determined by irradiating aliphatic acid silver salt dispersed in a solution with a laser ray and determining an autocorrelation function of the fluctuation of the scattered light on the basis of the change in time.
Methods for production and dispersion of the silver salt of an organic acid used for the present invention are not particularly limited, and various known methods can be used. For example, one can refer to the methods described in the aforementioned JP-A-10-62899, EP0803763A1, EP0962812A1, JP-A-11-349591, JP-A-2000-7683, JP-A-2000-72711, Japanese Patent Application Nos. 11-348228 to 11-348230, 11-203413, 2000-90093, 2000-195621, 2000-191226, 2000-213813, 2000-214155, 2000-191226 and so forth.
In the present invention, although the silver salt of an organic acid can be used in a desired amount, the amount in terms of silver is preferably 0.1-5 g/m2, more preferably 0.3-3 g/m2, further preferably 0.5-2 g/m2.
The photothermographic material of the present invention preferably contains a reducing agent for the non-photosensitive silver source (preferably silver salt of an organic acid). When a silver salt of an organic acid is used as the non-photosensitive silver source, the reducing agent may be any substance (preferably, organic substance) capable of reducing silver ions into metal silver. Examples of the reducing agent are described in JP-A-11-65021, paragraphs 0043 to 0045, EP0803764A1, from page 7, line 34 to page 18, line 12. In the present invention, preferably used as the reducing agent are the so-called hindered phenol type reducing agents and bisphenol type reducing agents, which have a substituent at the ortho-position of phenolic hydroxyl group, and it is more preferable to use a compound represented by the following formula (R). 
In the aforementioned formula (R), R11 and R11xe2x80x2 each independently represent an alkyl group having 1-20 carbon atoms. R12, R12xe2x80x2, R13, R13xe2x80x2, R14 and R14xe2x80x2 each independency represent a hydrogen atom or a substituent that can substitute on a benzene ring. L represents a xe2x80x94Sxe2x80x94 group or a xe2x80x94CHR15xe2x80x94 group. R15 represents a hydrogen atom or an alkyl group having 1-20 carbon atoms.
The formula (R) will be explained in detail.
R11 and R11xe2x80x2 each independently represent a substituted or unsubstituted alkyl group having 1-20 carbon atoms. Although the substituent of the alkyl group is not particularly limited, preferred examples thereof include an aryl group, a hydroxy group, an alkoxy group, an aryloxy group, an alkylthio group, an arylthio group, an acylamino group, a sulfonamido group, a sulfonyl group, a phosphoryl group, an acyl group, a carbamoyl group, an ester group, a ureido group, a urethane group, a halogen atom and so forth. The alkyl group may be linear or branched, and it may also be a cyclic cycloalkyl group.
R12, R12xe2x80x2, R13, R13xe2x80x2, R14 and R14xe2x80x2 each independency represent a hydrogen atom or a substituent that can substitute on a benzene ring. Preferred examples of the substituent that can substitute on a benzene ring include an alkyl group, an aryl group, a halogen atom, an alkoxy group and an acylamino group.
L represents a xe2x80x94Sxe2x80x94 group or a xe2x80x94CHR15xe2x80x94 group. R15 represents a hydrogen atom or an alkyl group having 1-20 carbon atoms, and the alkyl group may have a substituent. Examples of the unsubstituted alkyl group represented by R15 include methyl group, ethyl group, propyl group, butyl group, heptyl group, undecyl group, isopropyl group, 1-ethylpentyl group, 2,4,4-trimethylpentyl group and so forth. Examples of the substituent of the alkyl group are similar to the examples of the substituent of R11 and R11xe2x80x2.
R11 and R11xe2x80x2 preferably represent a secondary or tertiary alkyl group having 3-15 carbon atoms, and specific examples thereof include isopropyl group, isobutyl group, t-butyl group, t-amyl group, t-octyl group, cyclohexyl group, cyclopentyl group, 1-methylcyclohexyl group, 1-methylcyclopropyl group and so forth. R11 and R11xe2x80x2 more preferably represent a tertiary alkyl group having 4-12 carbon atoms, further preferably t-butyl group, t-amyl group or 1-methylcyclohexyl group, most preferably t-butyl group.
R12 and R12xe2x80x2 preferably represents an alkyl group having 1-20 carbon atoms, and specific examples thereof include methyl group, ethyl group, propyl group, butyl group, isopropyl group, t-butyl group, t-amyl group, cyclohexyl group, 1-methylcyclohexyl group, benzyl group, methoxymethyl group, methoxyethyl group and so forth. R12 and R12xe2x80x2 more preferably represents methyl group, ethyl group, propyl group, isopropyl group or t-butyl group. R13, R13xe2x80x2, R14 and R14xe2x80x2 preferably represent a hydrogen atom, a halogen atom or an alkyl group, more preferably a hydrogen atom.
L is preferably a xe2x80x94CHR15xe2x80x94 group. R15 is preferably a hydrogen atom or an alkyl group having 1-15 carbon atoms, and preferred examples of the alkyl group include methyl group, ethyl group, propyl group, isopropyl group and 2,4,4-trimethylpentyl group. R15 is particularly preferably a hydrogen atom, methyl group, ethyl group, propyl group or isopropyl group.
When R15 is a hydrogen atom, R12 and R12xe2x80x2 preferably represents an alkyl group having 2-5 carbon atoms, more preferably ethyl group or propyl group, most preferably ethyl group. When R15 is a primary or secondary alkyl group having 1-8 carbon atoms, R12 and R12xe2x80x2 preferably represents methyl group. The primary or secondary alkyl group having 1-8 carbon atoms represented by R15 is preferably methyl group, ethyl group, propyl group or isopropyl group, further preferably methyl group, ethyl group or propyl group.
When R11, R11xe2x80x2, R12 and R12xe2x80x2 all represent methyl group, R15 preferably represents a secondary alkyl group. In this case, the secondary alkyl group represented by R15 is preferably isopropyl group, isobutyl group or 1-ethylpentyl group, more preferably isopropyl group.
The reducing agent represented by the aforementioned formula (R) shows different heat development characteristic, developed silver color tone and so forth depending on a combination of substituents including R11, R11xe2x80x2, R12, R12xe2x80x2, R15 etc. It is also possible to obtain desired heat development characteristic or developed silver color tone by using two or more kinds of reducing agents in combination.
Specific examples of the reducing agent of the present invention including the compounds represented by the aforementioned formula (R) are shown below. However, the present invention is not limited to these. 
In the present invention, the amount of the reducing agent is preferably 0.1-3.0 g/m2, more preferably 0.2-1.5 g/m2, further preferably 0.3-1.0 g/m2. The amount of the reducing agent is preferably 5-50 mole %, more preferably 8-30 mole %, further preferably 10-20 mole %, per mole of silver on the side having the image-forming layer. The reducing agent is preferably contained in the image-forming layer containing the non-photosensitive silver source.
The reducing agent may be contained in the photothermographic material by adding it to a coating solution in any form such as solution, emulsion dispersion and solid microparticle dispersion and forming a layer with the coating solution.
For preparing a coating solution by emulsion dispersing the reducing agent, there can be mentioned a method of mechanically preparing an emulsion dispersion by using an oil such as dibutyl phthalate, tricresyl phosphate, glyceryl triacetate and diethyl phthalate and an auxiliary solvent such as ethyl acetate or cyclohexanone. Further, as a method for solid microparticle dispersion, there can be mentioned a method for preparing solid microparticle dispersion by dispersing powder of the reducing agent in a suitable solvent such as water using a ball mill, colloid mill, vibration ball mill, sand mill, jet mill and roller mill, or by means of ultrasonic wave. In this operation, protective colloid (e.g., polyvinyl alcohol), surfactant (e.g., anionic surfactants such as sodium triisopropylnaphthalenesulfonate (mixture of those having three isopropyl groups on different positions)) and so forth may be used. In the aforementioned mills, beads such as zirconia beads are usually used as dispersion media, and Zr or the like eluted from such beads may contaminate the dispersion. Although the concentration of the contaminants depends of the dispersion conditions, it is usually in the range of 1-1000 ppm. Content of Zr of 0.05 g or less per 1 g of silver in the photosensitive material does not cause any practical problem.
An aqueous dispersion preferably contains a preservative (e.g., benzisothiazolinone sodium salt).
In the photothermographic material of the present invention, the sulfonamidophenol compounds represented by the formula (A) mentioned in JP-A-2000-267222 and JP-A-2000-330234, hindered phenol compounds represented by the formula (II) mentioned in JP-A-2001-92075, hydrazine compounds represented by the formula (I) mentioned in JP-A-10-62895 and JP-A-11-15116 or the formula (1) mentioned in Japanese Patent Application No. 2001-074278 and phenol or naphthol compounds represented by the formula (2) mentioned in g Japanese Patent Application No. 2000-76240 are preferably used as a development accelerator. These development accelerators are used in an amount in the range of 0.1-20 mol %, preferably 0.5-10 mol %, more preferably 1-5 mol %, with respect to the reducing agent. Although they can be introduced into the photothermographic material by a method similar to those used for introducing the reducing agent, they are particularly preferably introduced as a solid dispersion or emulsion dispersion. When they are added as an emulsion dispersion, they are preferably added as an emulsion dispersion prepared by emulsion dispersion using a high-boiling point solvent that is solid at an ordinary temperature and a low-boiling point auxiliary solvent or a so-called oilless emulsion dispersion that is not added with a high boiling-point solvent.
In the present invention, when a reducing agent having an aromatic hydroxyl group (xe2x80x94OH) is used, in particular when the reducing agent is any of the aforementioned bisphenols is used, it is preferable to use together a non-reducing compound having a group that can form a hydrogen bond with the aromatic hydroxyl group (henceforth referred to as xe2x80x9chydrogen bond-forming compoundxe2x80x9d). The hydrogen bond-forming compound is described in detail in EP1096310. In the present invention, it is preferable to use hydrogen bond-forming compounds represented by the following formula (D). 
In the formula (D), R21, R22 and R23 each independently represent an alkyl group, an aryl group, an alkoxy group, an aryloxy group, an amino group or a heterocyclic group, and these groups may or may not have one or more substituents. As specific examples of the hydrogen bond-forming compound, besides those mentioned above, those mentioned in EP1096310, Japanese Patent Application Nos. 2000-270498, 2001-124796 and so forth can be mentioned.
Specific examples of the hydrogen bond-forming compounds including those represented by the aforementioned formula (D) will be shown below. However, the present invention is not limited to these examples. 
The hydrogen bond-forming compound can be may be added to the photothermographic material by adding it to a coating solution in the form of solution, emulsion dispersion or solid microparticle dispersion and forming a coated layer with the coating solution, like the reducing agent. The hydrogen bond-forming compound (preferably a compound represented by the aforementioned formula (D)) is preferably used in an amount of 1-200 mole %, more preferably 10-150 mole %, further preferably 20-100 mole %, with respect to the reducing agent.
The photothermographic material of the present invention contains silver halide. The silver halide is a photosensitive silver halide. It is not particularly limited as for the halogen composition, and silver chloride, silver chlorobromide, silver bromide, silver iodobromide and silver chloroiodobromide may be used. Among these, silver bromide and silver iodobromide are preferred. The halide composition may have a uniform distribution in the grains, or the compositions may change stepwise or continuously in the grains. Silver halide grains having a core/shell structure may be preferably used. Core/shell grains having preferably a double to quintuple structure, more preferably a double to quadruple structure may be used. A technique for localizing silver bromide on the surface of silver chloride or silver chlorobromide grains may also be preferably used.
Methods for the preparation of the photosensitive silver halide are well known in the art, and there can be used, for example, the methods described in Research Disclosure, No. 17029 (June, 1978) and U.S. Pat. No. 3,700,458. More specifically, a method can be used which comprises preparing photosensitive silver halide grains by addition of a silver-supplying compound and a halogen-supplying compound to a solution of gelatin or other polymer, and then mixing the resulting grains with a silver salt of an organic acid. The methods disclosed in JP-A-119374, paragraphs 0217 to 0224, JP-A-11-352627 (Japanese Patent Application No. 11-98708) and JP-A-2000-347335 are also preferred.
As for a grain size of the photosensitive silver halide, smaller grains are preferred to prevent cloudiness after image formation. Specifically, the grain size may preferably be not greater than 0.20 xcexcm, more preferably 0.01-0.15 xcexcm, further preferably 0.02-0.12 xcexcm. The term xe2x80x9cgrain sizexe2x80x9d used herein means a diameter of a circle having the same area of a projected area of the grain (where silver halide grains are tabular grains, projected area of the main plane is used).
Examples of the form of silver halide grains include a cubic form, octahedral form, tabular form, spherical form, rod-like form, potato-like form and so forth. In particular, cubic grains are preferred for the present invention. Silver halide grains having round corners are also preferably used.
Silver halide grains having hexacyano-metal complex on their outermost surfaces are preferably used. Specific examples of the hexacyano-metal complex include [Fe(CN)6]4xe2x88x92, [Fe(CN)6]3xe2x88x92, [Ru(CN)6]4xe2x88x92, [Os(CN)6]4xe2x88x92, [Co(CN)6]3xe2x88x92, [Rh(CN)6]3xe2x88x92, [Ir(CN)6]3xe2x88x92, [Cr(CN)6]3xe2x88x92, [Re(CN)6]3xe2x88x92 and so forth. In the present invention, hexacyano-Fe complexes are preferred. The amount of the hexacyano-metal complex is preferably 1xc3x9710xe2x88x925 mole to 1xc3x9710xe2x88x922 mole, more preferably 1xc3x9710xe2x88x924 mole to 1xc3x9710xe2x88x923 mole, per mole of silver.
The photosensitive silver halide grains used for the present invention may contain a metal of Group VIII to Group X in the periodic table of elements (including Group I to Group XVIII) or metal complex thereof. The metal of Group VIII to X of the periodic table or the center metal of the metal complex is preferably rhodium, ruthenium or iridium. The metal complex may be used alone, or two or more complexes of the same or different metals may also be used in combination. The content of the metal or metal complex is preferably from 1xc3x9710xe2x88x929 to 1xc3x9710xe2x88x923 mole per mole of silver. Such heavy metals and metal complexes as well as addition method therefor are described in JP-A-7-225449, JP-A-11-65021, paragraphs 0018 to 0024, and JP-A-11-119374, paragraphs 0227 to 0240.
Further, metal complexes that can be contained in the silver halide grains (e.g., [Fe(CN)6]4xe2x88x92), desalting methods and chemical sensitization methods are described in JP-A-11-84574, paragraphs 0046 to 0050, JP-A-11-65021, paragraphs 0025 to 0031, and JP-A-11-119374, paragraphs 0242 to 0250.
In the present invention, the photosensitive silver halide is contained in a photosensitive layer as a photosensitive silver halide emulsion. For the emulsion, various kinds of gelatin can be used. When the photosensitive silver halide and the silver salt of an organic acid are contained in the same layer, low molecular weight gelatin having a molecular weight of 500-60,000 is preferably used in order to obtain good dispersion state of the photosensitive silver halide emulsion in a coating solution containing a silver salt of an organic acid. While such low molecular weight gelatin may be used during the grain formation or the dispersion operation after the desalting treatment, it is preferably used during the dispersion operation after the desalting treatment.
In the present invention, a sensitizing dye is preferably used in order to spectrally sensitize the silver halide grains in a desired wavelength region. As the sensitizing dye, there can be used those sensitizing dyes which can adsorb on the silver halide grains and have spectral sensitivity suitable for spectral characteristics of the light source to be used for exposure. Such sensitizing dyes and addition methods therefor are described in JP-A-11-65021, paragraphs 0103 to 0109, JP-A-10-18657 as for the compounds represented by the formula (II), JP-A-11-119347 as for the dyes represented by the formula (I) and paragraph 0106, U.S. Pat. Nos. 5,510,236, 3,871,887 as for the dyes disclosed in Example 5, JP-A-2-96131, JP-A-59-48753 as for the dyes disclosed therein and EP 0803764A1, page 19, line 38 to page 20, line 35, Japanese Patent Application Nos. 2000-86865, 2000-102560, 2000-205399 and so forth. These dyes may be used each alone or in any combination of two or more of them. While the amount of the sensitizing dye used in the present invention may be selected to be a desired amount depending on the performance including sensitivity and fog, it is preferably 10xe2x88x926 to 1 mole, more preferably 10xe2x88x924 to 10xe2x88x921 mole, per mole of silver halide in the photosensitive layer.
A supersensitizer can be used in the present invention in order to improve spectral sensitization efficiency. Examples of the supersensitizer used for the present invention include the compounds disclosed in EP587338A, U.S. Pat. Nos. 3,877,943, 4,873,184, JP-A-5-341432, JP-A-11-109547, JP-A-10-111543 and so forth.
Photosensitive silver halide grains are preferably subjected to chemical sensitization by sulfur sensitization, selenium sensitization or tellurium sensitization. Any known compounds can be preferably used for such sulfur, selenium or tellurium sensitization, and for example, the compounds described in JP-A-7-128768 and so forth are usable for that purpose. Tellurium sensitization is particularly preferred for the present invention, and the compounds described in JP-A-11-65021, paragraph 0030 and the compounds of the formulas (II), (III) and (IV) given in JP-A-5-313284 are more preferred.
In the present invention, the chemical sensitization may be performed at any time so long as it is performed after the formation of the grains and before the coating. It may be performed after desalting and (1) before the spectral sensitization, (2) simultaneously with the spectral sensitization, (3) after the spectral sensitization, (4) immediately before the coating, or the like. It is particularly preferably performed after spectral sensitization. In the present invention, the amount of the sulfur, selenium or tellurium sensitizer varies depending on the type of the silver halide grains to be used, conditions for chemical ripening etc., but may fall generally between 10xe2x88x928 and 10xe2x88x922 mole, preferably between 10xe2x88x927 and 10xe2x88x923 mole or so, per mole of the silver halide. Although the conditions for the chemical sensitization are not particularly limited, in general, pH is in the range of 5-8, pAg is in the range of 6-11, and temperature is in the range of 40-95xc2x0 C. The silver halide emulsion used for the present invention may be added with a thiosulfonic acid compound according to the method disclosed in EP293917A.
In the photothermographic material of the present invention, one kind of photosensitive silver halide emulsion may be used or two or more different emulsions (for example, those having different average grain sizes, different halogen compositions, different crystal habits or those subjected chemical sensitization under different conditions) may be used in combination. By using plural photosensitive silver halides having different sensitivities, contrast can be controlled. Examples of the techniques concerning this respect include those mentioned in JP-A-57-119341, JP-A-53-106125, JP-A-47-3929, JP-A-48-55730, JP-A-46-5187, JP-A-50-73627, JP-A-57-150841 and so forth. Each emulsion preferably has sensitivity difference of 0.2 log E or higher for other emulsions.
The amount of the photosensitive silver halide is preferably 0.03-0.6 g/m2, more preferably 0.07-0.4 g/m2, most preferably 0.05-0.3 g/m2, as the amount of coated silver per 1 m2 of the photothermographic material. The amount of the photosensitive silver halide per mole of the silver salt of an organic acid is preferably 0.01-0.5 mole, more preferably 0.02-0.3 mole, further preferably 0.03-0.2 mole.
Methods and conditions for mixing photosensitive silver halide and a silver salt of an organic acid, which are separately prepared, are not particularly limited so long as the effect of the present invention can be attained satisfactorily. Examples thereof include, for example, a method of mixing silver halide grains and a silver salt of an organic acid after completion of respective preparations by using a high-speed stirring machine, ball mill, sand mill, colloid mill, vibrating mill, homogenizer or the like, or a method of preparing a silver salt of an organic acid by mixing a photosensitive silver halide obtained separately at any time during the preparation of the silver salt of an organic acid. For the mixing of them, mixing two or more kinds of aqueous dispersions of the silver salt of an organic acid and two or more kinds of aqueous dispersions of the photosensitive silver salt is preferably used for controlling photographic properties.
Preferred addition time point for the silver halide into a coating solution for image-forming layer resides in a period of from 180 minutes before the coating to immediately before the coating, preferably 60 minutes to 10 seconds before the coating. However, the method and conditions for mixing are not particularly limited so long as the effect of the present invention can be attained satisfactorily. Specific examples of the mixing method include a method in which the mixing is performed in a tank designed so that a desired average residence time therein can be obtained, which residence time is calculated from addition flow rate and feeding amount to a coater, a method utilizing a static mixer described in N. Harnby, M. F. Edwards, A. W. Nienow, xe2x80x9cEkitai Kongo Gijutsu (Techniques for Mixing Liquids)xe2x80x9d, translated by Koji Takahashi, Chapter 8, Nikkan Kogyo Shinbunsha, 1989 and so forth.
In the present invention, the binder of the layer containing the silver salt of an organic acid may be any polymer. Preferred binders are those that are transparent or translucent, and generally colorless. The binder may consist of, for example, a naturally occurring resin, polymer or copolymer, synthetic resin, polymer or copolymer or other media that can form a film, such as gelatins, rubbers, poly(vinyl alcohols), hydroxyethylcelluloses, cellulose acetates, cellulose acetate butyrates, poly(vinylpyrrolidones), casein, starch, poly(acrylic acids), poly(methyl methacrylates), poly(vinyl chlorides), poly(methacrylic acids), styrene/maleic anhydride copolymers, styrene/acrylonitrile copolymers, styrene/butadiene copolymers, poly(vinyl acetals) (e.g., poly(vinyl formal), poly(vinyl butyral)), poly(esters), poly(urethanes), phenoxy resin, poly(vinylidene chlorides), poly(epoxides), poly(carbonates), poly(vinyl acetates), poly(olefins), cellulose esters and poly(amides). The binder may be formed from water, organic solvent or emulsion by coating it.
In the present invention, the binder that can be used for the layer containing a silver salt of an organic acid preferably has a grass transition temperature (Tg) of 10-80xc2x0 C. (also referred to as xe2x80x9chigh Tg binderxe2x80x9d hereinafter), more preferably 15-70xc2x0 C., further preferably 20-65xc2x0 C.
In the present invention, polymers dispersible in aqueous solvents are particularly preferred. Although examples of systems in the dispersed state include, for example, latex in which fine particles of water-insoluble hydrophilic polymer are dispersed, and a system in which a polymer is dispersed in a molecular state or as micelles, particles dispersed as latex are preferred. Dispersed particles preferably have a mean particle size of around 1-50000 nm, more preferably around 5-1000 nm, further preferably 10-500 nm, particularly preferably 50-200 nm. Particle size distribution of the dispersed particles is not particularly limited, and either those having a broad particle size distribution or those having monodispersed particle size distribution may be used. A method of mixing two or more kinds of dispersion having monodispersed particle distribution and using the mixture is also a preferred method in view of control of physical properties of coating solution.
In the present invention, as preferred examples of the polymer dispersible in an aqueous solvent, hydrophobic polymers such as acrylic polymers, polyesters, rubbers (e.g., SBR resins), polyurethanes, polyvinyl chlorides, polyvinyl acetates, polyvinylidene chlorides, polyolefins and so forth can be used. The polymers may be linear, branched or crosslinked. They may be so-called homopolymers in which a single kind of monomer is polymerized, or copolymers in which two or more different kinds of monomers are polymerized. The copolymers may be random copolymers or block copolymers. The polymers may have a number average molecular weight of 5,000-1,000,000, preferably from 10,000-200,000. Polymers having a too small molecular weight fail to give sufficient mechanical strength of the emulsion layer, and those having a too large molecular weight yield bad film forming property, and both of which are not preferred. Further, crosslinked type polymer latex is particularly preferably used.
Specific examples of the preferred polymer latex are mentioned below. They are expressed with the constituent monomers. The numerals parenthesized indicate the contents in terms of weight %. The molecular weights are number average molecular weights. When multifunctional monomers are used, a crosslinked structure is formed and thus the concept of molecular weight cannot be applied. Therefore, for such a polymer, indication of xe2x80x9ccrosslinkedxe2x80x9d is appended and molecular weight is omitted. Tg indicates glass transition temperature.
P-1: Latex of -MMA(70)-EA(27)-MAA(3)-(molecular weight: 37000, Tg: 61xc2x0 C.)
P-2: Latex of -MMA(70)-2EHA(20)-St(5)-AA(5)-(molecular weight: 40000, Tg: 59xc2x0 C.)
P-3: Latex of -St(50)-Bu(47)-MMA(3)-(crosslinked, Tg: 17xc2x0 C.)
P-4: Latex of -St(68)-Bu(29)-AA(3)-(crosslinked, Tg: 17xc2x0 C.)
P-5: Latex of -St(71)-Bu(26)-AA(3)-(crosslinked, Tg: 24xc2x0 C.)
P-6: Latex of -St(70)-Bu(27)-IA(3)-(crosslinked)
P-7: Latex of -St(75)-Bu(24)-AA(1)-(crosslinked, Tg: 29xc2x0 C.)
P-8: Latex of -St(60)-Bu(35)-DVB(3)-MAA(2)-(crosslinked)
P-9: Latex of -St(70)-Bu(25)-DVB(2)-AA(3)-(crosslinked)
P-10: Latex of -VC(50)-MMA(20)-EA(20)-AN(5)-AA(5)-(molecular weight: 80000)
P-11: Latex of -VDC(85)-MMA(5)-EA(5)-MAA(5)-(molecular weight: 67000)
P-12: Latex of -Et(90)-MAA(10)-(molecular weight: 12000)
P-13: Latex of -St(70)-2EHA(27)-AA(3)-(molecular weight: 130000, Tg: 43xc2x0 C.)
P-14: Latex of -MMA(63)-EA(35)-AA(2)-(molecular weight: 33000, Tg: 47xc2x0 C.)
P-15: Latex of -St(70.5)-Bu(26.5)-AA(3)-(crosslinked, Tg: 23xc2x0 C.)
P-16: Latex of -St(69.5)-Bu(28.5)-AA(3)-(crosslinked, Tg: 20.5xc2x0 C.)
Abbreviations used in the above structures represents following monomers:
MMA: methyl methacrylate
EA: ethyl acrylate
MAA: methacrylic acid
2EHA: 2-ethylhexyl acrylate
St: styrene
Bu: butadiene
AA: acrylic acid
DVB: divinylbenzene
VC: vinyl chloride
AN: acrylonitrile
VDC: vinylidene chloride
Et: ethylene
IA: itaconic acid
The polymer latexes mentioned above are also commercially available, and those mentioned below can be used, for example. Examples of acrylic resins are CEBIAN A-4635, 46583, 4601 (all from Daicel Chemical Industries), Nipol Lx811, 814, 821, 820, 857 (all from Nippon Zeon) etc.; examples of polyester resins are FINETEX ES650, 611, 675, 850 (all from Dai-Nippon Ink and Chemicals), WD-size, WMS (both from Eastman Chemical) etc.; examples of polyurethane resins are HYDRAN AP10, 20, 30, 40 (all from Dai-Nippon Ink and Chemicals) etc.; examples of rubber resins are LACSTAR 7310K, 3307B, 4700H, 7132C (all from Dai-Nippon Ink and Chemicals), Nipol Lx416, 410, 438C, 2507 (all from Nippon Zeon) etc.; examples of polyvinyl chloride resins are G351, G576 (both from Nippon Zeon) etc.; examples of polyvinylidene chloride resins are L502, L513 (both from Asahi Chemical Industry) etc.; examples of polyolefin resins are CHEMIPEARL S120, SA100 (both from Mitsui Petrochemical) etc.
These polymer latexes may be used each alone, or two or more kinds of them may be blended as required.
As the polymer latex used in the present invention, styrene/butadiene copolymer latex is particularly preferred. In the styrene/butadiene copolymer, the weight ratio of styrene monomer units and butadiene monomer units is preferably 40:60 to 95:5. The ratio of the styrene monomer units and the butadiene monomer units preferably account for from 60-99 weight % of the copolymer. The polymer latex preferably contains 1-6 weight %, more preferably 2-5 weight %, of acrylic acid or methacrylic acid with respect to the sum of the styrene and butadiene. Further, polymer latex containing acrylic acid is also preferred.
Examples of styrene/butadiene copolymer latexes preferably used for the present invention include the aforementioned P-3 to P-8and P-15, commercially available products, LACSTAR-3307B, 7132C, Nipol Lx416 and so forth.
The layer containing the non-photosensitive silver source (preferably a silver salt of an organic acid) of the photothermographic material of the present invention may optionally be added with a hydrophilic polymer such as gelatin, polyvinyl alcohol, methylcellulose, hydroxypropylcellulose and carboxymethylcellulose. The amount of the hydrophilic polymer is preferably 30% by weight or less, more preferably 20% by weight or less, of the total binder in the layer containing silver salt of an organic acid.
In the present invention, the layer containing silver salt of an organic acid (i.e., the image-forming layer) is preferably formed by using polymer latex. The amount of the binder in the layer containing a silver salt of an organic acid may be 1/10 to 10/1, more preferably 1/3 to 5/1, further preferably 1/1 to 3/1, as indicated by a weight ratio of total binder/silver salt of an organic acid.
In the photothermographic material of the present invention, the layer containing the silver salt of an organic acid may also serve as a photosensitive layer (an emulsion layer) containing a photosensitive silver halide as a photosensitive silver salt. In that case, the weight ratio of total binder/silver halide may preferably be 400-5, more preferably 200-10.
The total amount of the binder in the image-forming layer of the photothermographic material of the present invention is preferably 0.2-30 g/m2, more preferably 1-15 g/m2, further preferably 2-10 g/m2. The image-forming layer may optionally be added with a crosslinking agent for crosslinking, a surfactant for improving coating property of a coating solution and so forth.
In the present invention, the solvent for the coating solution for the layer containing silver salt of an organic acid (for simplicity, a solvent as well as a dispersion medium are herein referred to as a xe2x80x9csolventxe2x80x9d) is preferably an aqueous solvent containing at least 30% by weight of water. As components other than water, any water-miscible organic solvents may be used such as, for example, methyl alcohol, ethyl alcohol, isopropyl alcohol, methyl cellosolve, ethyl cellosolve, dimethylformamide, ethyl acetate and so forth. The water content of the solvent for the coating solution is preferably at least 50% by weight, more preferably at least 70% by weight. Preferred examples of the solvent composition, besides water, include water/methyl alcohol=90/10, water/methyl alcohol=70/30, water/methyl alcohol/dimethylformamide=80/15/5, water/methyl alcohol/ethyl cellosolve=80/10/5, water/methyl alcohol/isopropyl alcohol=85/10/5 and so forth (numerals indicate weight %).
As antifoggants, stabilizers and stabilizer precursors that can be used for the present invention, there can be mentioned, for example, those mentioned in JP-A-10-62899, paragraph 0070 and EP0803764A1, from page 20, line 57 to page 21, line 7 as well as the compounds described in JP-A-9-281637, JP-A-9-329864, U.S. Pat. Nos. 6,083,681 and EP1048975. Antifoggants preferably used for the present invention are organic halogenated compounds. Examples thereof include, for example, those disclosed in JP-A-11-65021, paragraphs 0111 to 0112. Particularly preferred are the polyhalogenated compounds represented by the formula (P) mentioned in JP-A-2000-284399, the organic polyhalogenated compounds represented by the formula (II) mentioned in JP-A-10-339934, the organic polyhalogenated compounds described in JP-A-2001-31644 and JP-A-2001-33911.
Organic polyhalogenated compounds preferably used for the present invention will be specifically explained hereafter. In the present invention, it is preferable to use organic polyhalogenated compounds represented by the following formula (H).
Qxe2x80x94(Y)nxe2x80x94C (Z11)(Z12)xe2x80x94X xe2x80x83xe2x80x83Formula (H). 
In the aforementioned formula (H), Q represents an alkyl group, an aryl group or a heterocyclic group, Y represents a divalent bridging group, n represents 0 or 1, Z11 and Z12 represent a halogen atom, and X represents a hydrogen atom or an electron withdrawing group.
In the aforementioned formula (H), Q preferably represents a phenyl group substituted with an electron withdrawing group having a positive value of Hammett""s substituent constant sp. As for the Hammett""s substituent constant, Journal of Medicinal Chemistry, 1973, Vol. 16, No.11, 1207-1216 and so forth can be referred to. X preferably represents an electron withdrawing group, more preferably a halogen atom; an aliphatic, aryl or heterocyclylsulfonyl group; an aliphatic, aryl or heterocyclylacyl group; an aliphatic, aryl or heterocyclyloxycarbonyl group; a carbamoyl group; or a sulfamoyl group, further preferably a halogen atom. As the halogen atom, a chlorine atom, bromine atom and iodine atom are preferred, a chlorine atom and bromine atom are further preferred, and a bromine atom is particularly preferred. Y preferably represents xe2x80x94C(xe2x95x90O)xe2x80x94, xe2x80x94SOxe2x80x94 or xe2x80x94SO2xe2x80x94, more preferably xe2x80x94C(xe2x95x90O)xe2x80x94 or xe2x80x94SO2xe2x80x94, particularly preferably xe2x80x94SO2xe2x80x94. n represents 0 or 1, preferably 1.
Specific examples of the organic polyhalogenated compounds represented by the aforementioned formula (H) are shown below. However, the present invention is not limited by the following examples at all. 
The compound represented by the aforementioned formula (H) is preferably used in an amount of 10xe2x88x924 to 1 mole, more preferably 10xe2x88x923 to 0.5 mole, further preferably 10xe2x88x922 to 0.2 mole, per one mole of the non-photosensitive silver source contained in the image-forming layer.
As the method for introducing an antifoggant into the photothermographic material of the present invention, the aforementioned method for introducing the reducing agent can be mentioned. The organic polyhaogenated compound is also preferably added in the form of solid microparticle dispersion.
Other examples of the antifoggant include the mercury(II) salts described in JP-A-11-65021, paragraph 0113, the benzoic acids described in the same, paragraph 0114, the salicylic acid derivatives described in JP-A-2000-206642, the formalin scavenger compounds represented by the formula (S) mentioned in JP-A-2000-221634, the triazine compounds mentioned in JP-A-11-352624, claim 9, the compounds represented by the formula (III) mentioned in JP-A-6-11791, 4-hydroxy-6-methyl-1,3,3a,7-tetrazaindene and so forth.
The photothermographic material may contain an azolium salt for prevention of fog. Examples of the azolium salt include, for example, the compounds of the formula (XI) disclosed in JP-A-59-193447, the compounds disclosed in JP-B-55-12581 and the compounds of the formula (II) disclosed in JP-A-60-153039.
The photothermographic material of the present invention may optionally contain a mercapto compound, disulfide compound or thione compound to accelerate, suppress or control development, or increase efficiency in spectral sensitivity, or to improve storability before and after development. Examples thereof include, for example, those compounds described in JP-A-10-62899, paragraphs 0067 to 0069, compounds represented by s and specific examples thereof mentioned in JP-A-10-186572, paragraphs 0033 to 0052, and those described in EP0803764A1, page 20, lines 36 to 56. Among them, the mercapto-substituted heteroaromatic compounds described in JP-A-9-297367, JP-A-9-304875, JP-A-2001-100358 and so forth are preferred.
A toning agent is preferably added to the photothermographic material of the present invention. Examples of the toning agent are described in JP-A-10-62899, paragraphs 0054 to 0055, EP0803764A1, page 21, lines 23 to 48 and JP-A-2000-356317 and Japanese Patent Application No. 2000-187298. In particular, preferred are phthalazinones, combinations of phthalazinones and phthalic acids, phthalazines and combinations of phthalazines and phthalic acids, especially combinations of phthalazines and phthalic acids. Particularly preferred among these is a combination of 6-isopropylphthalazine and phthalic acid or 4-methylphthalic acid.
The photosensitive layer of the photothermographic material of the present invention may contain a plasticizer or lubricant. Plasticizers and lubricants are described in JP-A-11-65021, paragraph 0117. Ultrahigh contrast agents for forming ultrahigh contrast images and addition methods and amounts therefor are described in the same publication, paragraph 0118, JP-A-11-223898, paragraphs 0136 to 0193, JP-A-2000-284399, compounds of the formula (H), formulas (1) to (3), formulas (A) and (B) and those mentioned in Japanese Patent Application No. 11-91652 as compounds of the formulas (III) to (V) (specific compounds: Chemical Formulas 21 to 24); and contrast promoters are described in JP-A-11-65021, paragraph 0102, and JP-A-11-223898, paragraphs 0194 to 0195.
When formic acid or a formic acid salt is used as a strongly fogging substance, it is preferably used on the side having the image-forming layer containing a photosensitive silver halide in an amount of 5 mmol or less, more preferably 1 mmol or less, per 1 mole of silver.
When an ultrahigh contrast agent is used in the photothermographic material of the present invention, an acid formed by hydration of diphosphorus pentoxide or a salt thereof is preferably used together with the ultrahigh contrast agent. Examples of the acid formed by hydration of diphosphorus pentoxide or a salt thereof include metaphosphoric acid (salt), pyrophosphoric acid (salt), orthophosphoric acid (salt), triphosphoric acid (salt), tetraphosphoric acid (salt), hexametaphosphoric acid (salt) and so forth. Particularly preferably used acids formed by hydration of diphosphorus pentoxide or salts thereof are orthophosphoric acid (salt) and hexametaphosphoric acid (salt). Specific examples of the salt are sodium orthophosphate, sodium dihydrogenorthophosphate, sodium hexametaphosphate, ammonium hexametaphosphate and so forth. The acid formed by hydration of diphosphorus pentoxide or a salt thereof may be used in a desired amount (coating amount per 1 m2 of the photothermographic material) depending on the desired performance including sensitivity and fog. However, it can be used in an amount of preferably 0.1-500 mg/m2, more preferably 0.5-100 mg/m2.
The photothermographic material may be provided with a surface protective layer, for example, to prevent adhesion of dusts to the image-forming layer. The surface protective layer may consist of a single layer or a plurality of layers. The surface protective layer is described in, for example, JP-A-11-65021, paragraphs 0119 to 0120 and Japanese Patent Application No. 2000-171936. While gelatin is preferred as the binder in the surface protective layer, polyvinyl alcohol (PVA) is also preferably used or used together with gelatin. As the gelatin, for example, inert gelatin (e.g., Nitta Gelatin 750), phthalized gelatin (e.g., Nitta Gelatin 801) and so forth can be used. Preferred examples of PVA include, for example, those described in JP-A-2000-171936, paragraphs 0009 to 0020, completely saponified PVA, PVA-105, partially saponified PVA, PVA-205 and PVA-335, denatured polyvinyl alcohol, MP-203 (all from Kuraray Co., Ltd.) and so forth. The application amount of the polyvinyl alcohol (per m2 of the support) for protective layers is preferably 0.3-4.0 g/m2, more preferably 0.3-2.0 g/m2 (per one layer).
When the photothermographic material is used for, in particular, printing use in which dimensional change is critical, polymer latex is preferably used also in a protective layer or a back layer. Such latex is described in xe2x80x9cGosei Jushi Emulsion (Synthetic Resin Emulsion)xe2x80x9d, compiled by Taira Okuda and Hiroshi Inagaki, issued by Kobunshi Kanko Kai (1978); xe2x80x9cGosei Latex no Oyo (Application of Synthetic Latex)xe2x80x9d, compiled by Takaaki Sugimura, Yasuo Kataoka, Souichi Suzuki and Keishi Kasahara, issued by Kobunshi Kanko Kai (1993); Soichi Muroi, xe2x80x9cGosei Latex no Kagaku (Chemistry of Synthetic Latex)xe2x80x9d, Kobunshi Kanko Kai (1970) and so forth. Specific example thereof include latex of methyl methacrylate (33.5 weight %)/ethyl acrylate (50 weight %)/methacrylic acid (16.5 weight %) copolymer, latex of methyl methacrylate (47.5 weight %)/butadiene (47.5 weight %)/itaconic acid (5 weight %) copolymer, latex of ethyl acrylate/methacrylic acid copolymer, latex of methyl methacrylate (58.9 weight %)/2-ethylhexyl acrylate (25.4 weight %)/styrene (8.6 weight %)/2-hydroxyethyl methacrylate (5.1 weight %)/acrylic acid (2.0 weight %) copolymer, latex of methyl methacrylate (64.0 weight %)/styrene (9.0 weight %)/butyl acrylate (20.0 weight %)/2-hydroxyethyl methacrylate (5.0 weight %)/acrylic acid (2.0 weight %) copolymer and so forth. As for the binder of the surface protective layer, there may be used the combination of polymer latex disclosed in Japanese Patent Application No. 11-6872, and techniques disclosed in JP-A-2000-267226 (Japanese Patent Application No. 11-143058), paragraphs 0021-0025, Japanese Patent Application No. 11-6872, paragraphs 0027-0028, and JP-A-2000-19678 (Japanese Patent Application No. 10-199626), paragraphs 0023-0041. The ratio of the polymer latex in the surface protective layer with respect to the total binder is preferably 10-90 weight %, particularly preferably 20-80 weight %.
Coated amount of the total binder (including wafer-soluble polymer and latex polymer) in the surface protective layer (for one layer) is preferably 0.3-5.0 g/m2, more preferably 0.3-2.0 g/m2 (per m2 of the support).
The temperature for preparation of the coating solution for the image-forming layer of the present invention may preferably be 30-65xc2x0 C., more preferably 35-60xc2x0 C., most preferably 35-55xc2x0 C. The temperature of the coating solution immediately after the addition of the polymer latex may preferably be kept at 30-65xc2x0 C.
In the present invention, the image-forming layer is provided as one or more layers on the support. When it is provided as a monolayer, the layer must contain a non-photosensitive silver source (preferably a silver salt of an organic acid), photosensitive silver halide, reducing agent and binder, and it may contain additional materials such as toning agent, coating aid and other auxiliary agents. When the layer is bilayer, the first image-forming layer (in general, the layer adjacent to the support) must contain a silver salt of an organic acid and silver halide, and the second image-forming layer or said two layers must contain the other ingredients. Multicolor photothermographic material may contain these two layers for each color, or may contain all necessary ingredients in a single layer as described in U.S. Pat. No. 4,708,928. As for multicolor photothermographic materials containing multiple dyes, each emulsion layer is kept individually by using a functional or non-functional barrier layer between the adjacent photosensitive layers as described in U.S. Pat. No. 4,460,681.
In the image-forming layer of the present invention, various types of dyes and pigments may be used to improve color tone, to prevent interference fringes generated during laser exposure, and to prevent irradiation (e.g., C.I. Pigment Blue 60, C.I. Pigment Blue 64, C.I. Pigment Blue 15:6). These techniques are detailed in International Patent Publication WO98/36322, JP-A-10-268465, JP-A-11-338098 and so forth.
In the present invention, a colorant that shows absorption maximum in the range of 300-450 nm may be added in order to improve change of silver color tone and images with time. Such a colorant is described in JP-A-62-210458, JP-A-63-104046, JP-A-63-103235, JP-A-63-208846, JP-A-63-306436, JP-A-63-314535, JP-A-01-61745, JP-A-2001-100363 and so forth. Such a colorant is usually added in an amount of 0.1 mg/m2 to 1 g/m2, and it is preferably added to a back layer, which is provided on the side opposite to the side on which the photosensitive layer is provided.
The photothermographic material of the present invention is preferably a so-called single-sided photothermographic material comprising at least one image-forming layer containing a silver halide emulsion on one side of support, and a back layer on the other side.
In the present invention, the photothermographic material preferably contains a matting agent for improving the transferability of the material. Matting agents are described in JP-A-11-65021, paragraphs 0126 to 0127. The matting agent is preferably added in an amount of 1-400 mg/m2, more preferably 5-300 mg/m2, as the amount per 1 m2 of the photothermographic material. In the present invention, the matting agent may have a regular shape or irregular shape, but it preferably has a regular shape, and a spherical shape is preferably used. The matting agent preferably has a mean particle size of 0.5-10 xcexcm, more preferably 1.0-8.0 xcexcm, further preferably 2.0-6.0 xcexcm. The variation coefficient of size distribution is preferably 50% or less, more preferably 40% or less, further preferably 30% or less. The variation coefficient used herein means a value represented as (standard deviation of particle size)/(average of particle size)xc3x97100. It is also preferable to use together two kinds of matting agents having a small variation coefficient and a ratio of mean particle sizes larger than 3. While the matting degree of the surface of the emulsion layer is not particularly limited so long as the material is free from stardust defects, Beck""s smoothness of the surface is preferably 30-2000 seconds, more preferably 40-1500 seconds. Beck""s smoothness can be easily determined according to Japanese Industrial Standard (JIS) P8119, xe2x80x9cTest Method for Smoothness of Paper and Paperboard by Beck Test Devicexe2x80x9d and TAPPI Standard Method T479.
In an embodiment of the present invention utilizing a back layer, the matting degree of the back layer is preferably 10-1200 seconds, more preferably 20-800 seconds, further preferably 40-500 seconds, in terms of the Beck""s smoothness.
In the present invention, the matting agent is preferably incorporated in the outermost surface layer or a layer which functions as the outermost surface layer of the photothermographic material, or alternatively, in a layer close to the outer surface or a layer which acts as a so-called protective layer. The back layers that are applicable to the photothermographic material are described in JP-A-11-65021, paragraphs 0128 to 0130.
The photothermographic material of the present invention preferably has a film surface pH of 7.0 or less, more preferably 6.6 or less, before heat development. While the lower limit is not particularly defined, it is normally around 3. The most preferred pH range is 4-6.2. For controlling the film surface pH, an organic acid such as phthalic acid derivatives or a nonvolatile acid such as sulfuric acid, and a volatile base such as ammonia are preferably used to lower the film surface pH. In particular, ammonia is preferred to achieve a low film surface pH, because it is highly volatile and therefore it can be removed before coating or heat development. Further, a combination of a nonvolatile base such as sodium hydroxide, potassium hydroxide and lithium hydroxide and ammonia is also preferably used. A method for measuring the film surface pH is described in JP-A-2000-2843 (Japanese Patent Application No. 11-87297), paragraph 0123.
In the photothermographic material of the present invention, a hardening agent may be added to the photosensitive layer, protective layer, back layer and other layers. Examples of the hardening agent are described in T. H. James, xe2x80x9cTHE THEORY OF THE PHOTOGRAPHIC PROCESS, FOURTH EDITIONxe2x80x9d, Macmillan Publishing Co., Inc., 1977, pp. 77-87. There may be preferably used chromium alum, 2,4-dichloro-6-hydroxy-s-triazine sodium salt, N,N-ethylenebis-(vinylsulfonacetamide), N,N-propylenebis(vinylsulfonacetamide), as well as the polyvalent metal ions described on page 78 of the above article, polyisocyanates described in U.S. Pat. No. 4,281,060 and JP-A-6-208193; epoxy compounds described in U.S. Pat. No. 4,791,042; vinylsulfone compounds described in JP-A-62-89048 and so forth.
The hardening agent is added to a coating solution as a solution. Preferred addition time of the solution to the coating solution of the protective layer resides in a period of from 180 minutes before the coating to just before the coating, preferably 60 minutes to 10 seconds before the coating. The method and conditions for mixing are not particularly limited so long as the effect of the present invention can be sufficiently attained. Specific examples of the mixing method include a method in which a mixing is performed in a tank designed so as to obtain a desired average residence time which is calculated from addition flow rate and feeding amount to a coater, a method utilizing a static mixer described in N. Harnby, M. F. Edwards, A. W. Nienow, xe2x80x9cEkitai Kongo Gijutsu (Techniques for Mixing Liquids)xe2x80x9d, translated by Koji Takahashi, Chapter 8, Nikkan Kogyo Shinbunsha, 1989 and so forth.
Surfactants that can be used in the present invention are described in JP-A-11-65021, paragraph 0132; usable solvents are described in the above patent document in paragraph 0133; usable supports are described in the above patent document in paragraph 0134; usable antistatic and electroconductive layers are described in the above patent document in paragraph 0135; usable methods for forming color images are described in the above patent document in paragraph 0136; and lubricants are described in JP-A-11-84573, paragraphs 0061-0064 and Japanese Patent Application No. 11-106881, paragraphs 0049-0062.
The photothermographic material of the present invention preferably has an electroconductive layer containing a metal oxide. As a conductive material contained in the electroconductive layer, a metal oxide of which conductivity is increased by introducing oxygen defects or heterogenous metal atoms into the metal oxide is preferably used. Preferred examples of the metal oxide include ZnO, TiO2 and SnO2, and addition of Al or In to ZnO2, addition of Sb, Nb, P, a halogen element etc. to SnO2 and addition of Nb, Ta etc to TiO2 are preferred. SnO2 added with Sb is particularly preferred. The amount of heteroatoms is preferably in the range of 0.01-30 mol %, more preferably 0.1-10 mol %. Although the metal oxide may have any shape such as spherical form, acicular form and tabular form, acicular grains having a long axis/short axis ratio of 2.0 or more, preferably 3.0-50, are preferred in view of impartation of electroconductivity. The amount of the metal oxide is preferably in the range of 1-1000 mg/m2, more preferably 10-500 mg/m2, further preferably 20-200 mg/m2. Although the electroconductive layer according to the present invention may be disposed on either the emulsion layer side or the back side, it is preferably disposed between a support and a back layer. Specific examples of the electroconductive layer used for the present invention are described in JP-A-7-295146 and JP-A-11-223901. In the present invention, it is preferable to use a fluorine-containing surfactant. Specific examples of the fluorine-containing surfactant include the compounds described in JP-A-10-197985, JP-A-2000-19680, JP-A-2000-214554 and so forth. The polymer fluorine-containing surfactants described in JP-A-9-281636can also preferably be used. In the present invention, the fluorine-containing surfactants disclosed in Japanese Patent Application No. 2000-206560 are particularly preferably used.
Preferably used as a transparent support is a polyester film, in particular, polyethylene terephthalate film, subjected to a heat treatment in a temperature range of 130-185xc2x0 C. in order to relax the internal distortion formed in the film during the biaxial stretching so that thermal shrinkage distortion occurring during the heat development can be eliminated. When the photothermographic material is for medical use, the transparent support may be colored with blue dyes (e.g., with Dye-1 described in Examples of JP-A-8-240877), or may be colorless. For the support, techniques for undercoating described in JP-A-11-84574 (utilizing water-soluble polyester), JP-A-10-186565 (utilizing styrene/butadiene copolymer), JP-A-2000-39684 and Japanese Patent Application No. 11-106881, paragraphs 0063-0080 (utilizing vinylidene chloride copolymer) and so forth are preferably used. As for antistatic layers and undercoating, techniques disclosed in JP-A-56-143430, JP-A-56-143431, JP-A-58-62646, JP-A-56-120519, JP-A-11-84573, paragraphs 0040-0051, U.S. Pat. No. 5,575,957, JP-A-11-223898, paragraphs 0078-0084 and so forth can also be used.
The photothermographic material is preferably a monosheet type material (the monosheet type material uses no additional sheet such as an image receiving material, and can form images directly on the photothermographic material itself).
The photothermographic material may further contain an antioxidant, stabilizer, plasticizer, ultraviolet absorber or coating aid. Such additives may be added to any of photosensitive layers or non-photosensitive layers. For these additives, WO98/36322, EP803764A1, JP-A-10-186567, JP-A-10-18568 and so forth can be referred to.
In the preparation of the photothermographic material of the present invention, coating solutions for forming the layers may be coated by any methods. Specific examples thereof include various types of coating techniques, for example, extrusion coating, slide coating, curtain coating, dip coating, knife coating, flow coating, extrusion coating utilizing a hopper of the type described in U.S. Pat. No. 2,681,294 and so forth. Preferred examples include extrusion coating and slide coating described in Stephen F. Kistler, Petert M. Schweizer, xe2x80x9cLIQUID FILM COATINGxe2x80x9d, published by CHAPMAN and HALL Co., Ltd., 1997, pp.399-536, and the slide coating is most preferably used. An example of the shape of a slide coater used for the slide coating is shown in FIG. 11b, 1, on page 427 of the aforementioned reference. If desired, two or more layers may be formed at the same time, for example, according to the methods described from page 399 to page 536 of the aforementioned reference, or the methods described in U.S. Pat. No. 2,761,791 and British Patent No. 837,095.
The coating solution for a layer containing a silver salt of an organic acid used in the preparation of the photothermographic material of the present invention is preferably a so-called thixotropic flow. As for this technique, JP-A-11-52509 can be referred to. A coating solution for a layer containing a silver salt of an organic acid used in the present invention preferably has a viscosity of 400-100,000 mPaxc2x7s, more preferably 500-20,000 mPaxc2x7s, at a shear rate of 0.1 secxe2x88x921. The viscosity is preferably 1-200 mPaxc2x7s, more preferably 5-80 mPaxc2x7s, at a shear rate of 1000 secxe2x88x921.
Other techniques that can be used for the photothermographic material of the present invention are also described in EP803764A1, EP883022A1, WO98/36322, JP-A-56-62648, JP-A-58-62744, JP-A-9-43766, JP-A-9-281637, JP-A-9-297367, JP-A-9-304869, JP-A-9-311405, JP-A-9-329865, JP-A-10-10669, JP-A-10-62899, JP-A-10-69023, JP-A-10-186568, JP-A-10-90823, JP-A-10-171063, JP-A-10-186565, JP-A-10-186567, JP-A-10-186569, JP-A-10-186570, JP-A-10-186571, JP-A-10-186572, JP-A-10-197974, JP-A-10-197982, JP-A-10-197983, JP-A-10-197985, JP-A-10-197986, JP-A-10-197987, JP-A-10-207001, JP-A-10-207004, JP-A-10-221807, JP-A-10-282601, JP-A-10-288823, JP-A-10-288824, JP-A-10-307365, JP-A-10-312038, JP-A-10-339934, JP-A-11-7100, JP-A-11-15105, JP-A-11-24200, JP-A-11-24201, JP-A-11-30832, JP-A-11-84574, JP-A-11-65021, JP-A-11-109547, JP-A-11-125880, JP-A-11-129629, JP-A-11-133536, JP-A-11-133537, JP-A-11-133538, JP-A-11-133539, JP-A-11-133542, JP-A-11-133543, JP-A-11-223898, JP-A-11-352627, JP-A-11-305377, JP-A-11-305378, JP-A-11-305384, JP-A-11-305380, JP-A-11-316435, JP-A-11-327076, JP-A-11-338096, JP-A-11-338098, JP-A-11-338099, JP-A-11-343420, Japanese Patent Application Nos. 2000-187298, 2000-10229, 2000-47345, 2000-206642, 2000-98530, 2000-98531, 2000-112059, 2000-112060, 2000-112104, 2000-112064 and 2000-171936.
In order to suppress fluctuation of photographic performance during storage before use or improve curling or deformation due to rolling, the photothermographic material of the present invention is preferably packaged with a packaging material showing a low oxygen permeability and/or low moisture permeability. The oxygen permeability is preferably 50 mL/atmxc2x7m2xc2x7day or less, more preferably 10 mL/atmxc2x7m2xc2x7day or less, further preferably 1.0 mL/atmxc2x7m2xc2x7day or less, at 25xc2x0 C. The moisture permeability is preferably 10 g/atmxc2x7m2xc2x7day or less, more preferably 5 g/atmxc2x7m2xc2x7day or less, further preferably 1 g/atmxc2x7m2xc2x7day or less. Specific examples of such a packaging material showing a low oxygen permeability and/or low moisture permeability include the packaging materials disclosed in JP-A-8-254793 and JP-A-2000-206653.
Although the development method for the photothermographic material of the invention is not particularly limited, a photothermographic material exposed imagewise is usually developed by heating. The temperature for the development is preferably 80-250xc2x0 C., more preferably 100-140xc2x0 C., further preferably 110-130xc2x0 C. The development time is preferably 1-60 seconds, more preferably 3-30 seconds, further preferably 5-25 seconds, particularly preferably 7-15 seconds.
For the heat development, although either a drum heater or a plate heater may be used, preferred is a plate heater system. For heat development by the plate heater system, the method described in JP-A-11-133572 is preferred. The plate heater system described in this reference is a heat development apparatus wherein a photothermographic material on which a latent image is formed is brought into contact with heating means in a heat development section to obtain a visible image. In this apparatus, the heating means comprises a plate heater, and a plurality of presser rollers are disposed facing to one surface of the plate heater. Heat development of the photothermographic material is attained by passing the material between the presser rollers and the plate heater. The plate heater is preferably sectioned into 2 to 6 stages, and the temperature of the top stage is preferably kept lower by 1-10xc2x0 C. or so than that of the others. For example, four plate heaters are used, of which temperature can be independently controlled, and temperature of the heaters are controlled to be 112xc2x0 C., 119xc2x0 C., 121xc2x0 C. and 121xc2x0 C., respectively. Such a method is also described in JP-A-54-30032, and such a plate heater system can remove moisture and organic solvent contained in the photothermographic material out of the material, and prevent deformation of the support of the photothermographic material due to rapid heating of the material.
While the photothermographic material of the present invention can be exposed in any manner, as light source of exposure, laser rays are preferred. As the laser used in the present invention, gas lasers (Hexe2x80x94Ne), dye lasers, semiconductor lasers and so forth are preferred. A combination of semiconductor laser and second harmonic generating device may also be used. Preferred are gas or semiconductor lasers for red emission.
As an example of a laser imager for medical use provided with a light exposure section and a heat development section, Fuji Medical Dry Laser Imager FM-DP L can be mentioned. FM-DP L is explained in Fuji Medical Review, No. 8, pages 39-55, and the techniques described therein can of course be used in laser imagers for the photothermographic material of the present invention. Further, the photothermographic material of the present invention can be used as a photothermographic material for laser imagers in xe2x80x9cAD networkxe2x80x9d, which was proposed by Fuji Medical System as a network system that conforms to the DICOM standard.
The photothermographic material forms a monochromatic image based on silver image, and is preferably used as a photothermographic material for use in medical diagnosis, industrial photography, printing and COM.